Closed-Loop Neurostimulation Using ECAP Feedback at High Frequencies
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Solution Overview
Problem
Existing closed-loop spinal cord stimulation (SCS) technologies face limitations in measuring perceived stimulation strength at higher frequencies, require empirical patient-specific calibration, and are prone to interference between stimulation pulses and evoked compound action potential (ECAP) recordings, restricting frequency range to around 500 Hz.
Innovation Solution
A neurostimulation device with a closed-loop control system using a multiphase stimulation approach, employing a plurality of electrodes to deliver therapeutic and charge-balancing pulses, records ECAP signals, and adjusts pulse amplitude based on ECAP signals to achieve precise control, allowing concurrent stimulation and recording without interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ECAP recording is used for closed-loop control, then feedback control of neural stimulation is achieved, but stimulation pulse interferes with ECAP recording at frequencies above 500 Hz
Solution Approach 1:
The patent divides the electrode array into separate stimulation electrodes and recording electrodes. By spatially segmenting the functions of stimulation and recording, the system can deliver high-frequency stimulation pulses while simultaneously recording ECAPs without interference, as the recording electrodes are positioned to capture neural responses away from the direct stimulus artifact zone.
Solution Approach 2:
The patent uses charge-balancing pulses as an intermediary mechanism. These balancing pulses are delivered between therapeutic pulses to return the electrode-tissue interface to its resting potential, preventing charge accumulation that would otherwise interfere with ECAP recording. This intermediary action enables sustained high-frequency stimulation while maintaining recording fidelity.
2Measurement precision
If empirical patient-specific calibration is performed to determine therapeutic window, then accurate patient-specific control is achieved, but time-consuming clinic testing is required
Solution Approach 1:
The patent implements self-service calibration where the system automatically determines the patient-specific therapeutic window by utilizing the recorded ECAP signals. The closed-loop control system processes ECAP amplitudes to identify perception thresholds and sub-perception levels automatically, eliminating the need for lengthy manual clinic testing while maintaining patient-specific accuracy.
Solution Approach 2:
The system uses real-time feedback from ECAP recordings to dynamically determine the therapeutic window. By continuously monitoring ECAP amplitudes and comparing them against predefined thresholds, the system automatically identifies the range between sub-perception and supra-perception levels, providing accurate patient-specific calibration without external intervention.
3Extent of automation
If ECAP amplitude is used as control variable, then closed-loop control is implemented, but perceived stimulation strength cannot be extracted at supra-threshold levels
Solution Approach 1:
The patent changes the parameter used for control from raw ECAP amplitude to a processed metric that reflects perceived stimulation strength. By analyzing the relationship between ECAP amplitude and patient perception across different stimulation levels, the system derives a new control parameter that accurately represents perceived strength even at supra-threshold frequencies, enabling effective closed-loop control.
Solution Approach 2:
The patent replaces direct mechanical measurement of perception (patient feedback during clinic visits) with an electrical substitute - using processed ECAP signals as a proxy for perceived stimulation strength. This substitution allows the system to infer perception levels continuously from electrical recordings, eliminating the need for repeated patient feedback while maintaining accurate control.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables effective closed-loop control at higher frequencies, provides patient-specific therapeutic window estimation, and accounts for neurosynaptic dynamics, ensuring optimal amplitude and range adjustment for pain relief.
Implementation Method 1
deliver in a cycle via each electrode of a group of N electrodes of said plurality of Z electrodes a set of electric pulses including one therapeutic electric pulse, and a number of N or N−1 charge balancing pulses
Implementation Method 2
the neurostimulation device is configured to record for the respective therapeutic electric pulse at least one ECAP signal
Implementation Method 3
the neurostimulation device comprises a closed-loop control system configured to update the amplitude of the therapeutic electric pulse based on said ECAP signal
Data Source
AI summary
A neurostimulation device includes more than three Z electrodes and is configured to deliver, in a cycle via each electrode of a group of N electrodes of the Z electrodes, a set of electric pulses including one therapeutic electric pulse, and a number of N or N−1 charge balancing pulses. N is less than or equal to Z, where N is equal to three when Z is equal to three. The charge balancing electric pulses each have a polarity that is opposite a polarity of the therapeutic electric pulse. The integrated current delivered by the therapeutic electric pulse and charge balancing pulses is zero over time. The neurostimulation device is configured to record for the respective therapeutic electric pulse at least one ECAP signal. The neurostimulation device has a closed-loop control system configured to update an amplitude of the therapeutic electric pulse based on the ECAP signal.